Surge suppressor with a bracing element

ABSTRACT

The invention relates to a surge suppressor for a high voltage or a medium voltage. The pack of said surge suppressor consists of arrester elements ( 1, 2, 3 ) and terminal armatures ( 4, 5 ) and is axially held together by means of bracing elements ( 6, 7, 8 ) in the form of epoxy resin rods. Said bracing elements ( 6, 7, 8 ) are held in the terminal armatures in a self-locking manner by means of conical bracing cylinders ( 9, 10, 11, 12, 13, 14 ). Said bracing cylinders are arrested on the bracing elements ( 6, 7, 8 ) when a tensile force is applied in the conical bores of the terminal armatures.

The invention relates to a surge arrester having at least onedissipation element, which is arranged between two electricallyconductive end fittings, and having at least one bracing element, whichis attached to the two end fittings and, in the axial direction, holdstogether the stack formed from the dissipation element and the endfittings.

A surge arrester such as this is known, for example, from JapanesePatent Application No. 62/149511.

In that document, a number of dissipation elements are combined to forma cylindrical stack, which also has an end fitting at each of its ends,with the end fittings having recesses for bracing elements in the formof rods. The bracing elements are braced between the end fittings bymeans of threaded nuts, with the threaded nuts resting on the edges ofthe recesses of the end fittings.

When assembling such a surge arrester, the individual nuts must bescrewed tight, and a uniform pressure distribution should be ensured onthe circumference of the end fittings.

The present invention is based on the object of simplifying the assemblyprocess and of reliably bracing the stack for a surge arrester of thetype mentioned initially.

According to the invention, the object is achieved in that the bracingelement is held in a bracing sleeve in at least one end fitting, in thatthe external contour of the bracing sleeve tapers conically in the axialdirection toward the center of the stack in a conical region, in thatthe bracing sleeve has a hole for holding a bracing element, theboundary walls of which hole can move toward the interior of the hole atleast in the conical region, and in that the end fitting has a recesspassing through it, for holding in each case one clamping sleeve, intowhich recess the respective clamping sleeve can be at least partiallypushed, with the conical region being deformed.

For attachment to the end fitting, the bracing element can be pushedinto the bracing sleeve, which is then inserted into the recess passingthrough it, within the end fitting. The already assembled stack is thenfixed, and a tensile stress is applied to the bracing element. Thiselastically lengthens the bracing element. The spring stress in thebracing element is stored by at least one spacer in the stackcompensating for the bracing movement. Such a spacer may be provided,for example, by a spacing screw which can move between an end fittingand the dissipation elements. The bracing sleeve can be pushed into therecess passing through the end fitting until the conical region of thebracing sleeve abuts against the walls of the recess passing through theend fitting, so that the boundary walls start to move radially towardthe hole interior onto the bracing element.

This further deforms the conical region of the bracing sleeve, and theboundary walls are pressed radially inward onto the bracing element. Thebracing element is thus held in the bracing sleeve by a force fit. To dothis, the dimensions and shapes of the recess passing through the endfitting and of the bracing sleeve must be appropriately matched to oneanother. The conicity of the bracing sleeve must likewise be suitablyconfigured.

The bracing element advantageously consists of a fiber-reinforced epoxyresin. The radial introduction of force into the bracing element bymeans of the force fit with respect to the bracing sleeve firstlyresults in there being no notch effect on the bracing element while,secondly, virtually the entire cross section of the bracing element isused to transmit the axial force. The axial bracing of the stackautomatically holds the bracing element in the bracing sleeve.

It is advantageously possible to provide for the recess passing throughthe end fitting to be designed to be complementary to the conical regionof the bracing sleeve.

This means that it is particularly simple to compress the bracing sleevein the desired manner while exerting axial tension toward the bracingelement.

Furthermore, it is advantageously possible to provide for the bracingsleeve to be slotted in the conical region, so that the boundary wallsof the hole can move in a radially sprung manner in the conical region.

The slotting in the bracing sleeve makes it particularly simple for theboundary walls of the hole to move radially in the bracing sleeve.

A further advantageous refinement of the invention provides for thebracing element to be held by means of a bracing sleeve in each of theend fittings.

It is also advantageously possible to provide for a number of bracingelements to be provided, parallel to the axis of the stack, on itsexternal circumference.

This makes it possible to distribute the large axial forces in thedissipation stack well between a number of bracing elements. The uniformdistribution of the tensile forces between the various bracing elementsis produced automatically. Furthermore, the use of a number of bracingelements results in greater mechanical strength.

It is also advantageously possible to provide for the end fittings toproject radially beyond the dissipation elements and, in the projectingregion, to have conical holes for holding the respective bracingsleeves.

In this way, the bracing elements can be used to form a cage whichsurrounds the dissipation elements and which, for example, can beencapsulated with a silicone elastomer, together with the dissipationelements, while the surge arrester is being manufactured.

In addition, it is advantageously possible to provide for each bracingsleeve to have a hole whose shape is designed to form an accurate fitwith the external contour of the respective bracing element.

This allows a particularly effective force fit to be achieved betweenthe respective bracing sleeve and the bracing element.

In the following text, the invention will be illustrated using anexemplary embodiment in a drawing, and will then be described.

In the figures:

FIG. 1 shows a schematic view of a surge arrester,

FIG. 2 shows the view of a bracing sleeve.

FIG. 1 shows schematically, the surge arrester with a stack comprisingthe dissipation elements 1, 2, 3 and the end fittings 4, 5. Thedissipation elements are composed, for example, of zinc oxide. Eachdissipation element is metallized on its end surfaces, so that axialcompression of the end fittings 4, 5 and of the dissipation elements 1,2, 3 results in a conductive connection between the dissipationelements. When dissipation occurs, that is to say when the voltageapplied to the surge arrester exceeds a critical value, a dissipationcurrent can then flow from one end fitting 4 via the dissipationelements 1, 2, 3 to the other end fitting.

The bracing elements 6, 7, 8 are provided in order to brace the stackand are in the form of rods having a circular cross section and composedof fiber-reinforced epoxy resin. The reinforcing fibers may, forexample, be glass fibers.

At their ends, the bracing elements 6, 7, 8 are each held in a bracingsleeve 9, 10, 11, 12, 13, 14.

As FIG. 2 shows, each bracing sleeve is in the form of a hollow cylinderand has a conical region 15 which tapers conically axially toward thecenter of the stack.

In its interior, the bracing sleeve 9 has a hole 20, which is matched toform an accurate fit with the external contour of a clamping element 6.

Slots 16, 17, 18, 19, which pass through the bracing sleeve 9, areprovided in it in the conical region 15, and allow the boundary walls21, 22, 23, 24 of the hole 20 which passes through the bracing sleeve 9to move in a sprung manner in the conical region 15, radially withrespect to the longitudinal axis of the bracing sleeve 9.

Each of the end fittings 4, 5 has recesses in the form of conical holes,each of which holds a bracing sleeve 9, 10, 11, 12, 13, 14.

When tensile forces are applied to the bracing elements 6, 7, 8, thebracing sleeves 9, 10, 11, 12, 13, 14 are drawn into the conical holesin the end fittings, so that the boundary walls 21, 22, 23, 24 arepressed inward onto the respective bracing element 6, 7, 8, which isheld in the bracing sleeve 9, 10, 11, 12, 13, 14, and are fixed with aforce fit.

This force-fitting joint between the respective bracing element 6, 7, 8and the clamping sleeve means that the tensile force is introduced in anoptimum manner into the bracing elements 6, 7, 8, so that they areloaded uniformly over their entire cross section.

The procedure for assembly of such a surge arrester comprises the stack1, 2, 3, 4, 5 being assembled in advance first of all, the bracingelements 6, 7, 8 and the corresponding bracing sleeves being pushed in,and, after this, the bracing elements being lengthened axially. Theincrease in length is compensated for by screwing in a contact screw,which is supported on a dissipation element or on a metal plate adjacentto it, and is guided in a thread in an end fitting. The spring forcewhich is stored in the bracing elements in this way thus results in thedissipation elements being compressed axially all the time.

What is claimed is:
 1. A surge arrester, comprising: at least onedissipation element arranged between two electrically conductive endfittings; and at least one bracing element attached to the two endfittings and, in an axial direction, holds together a stack formed fromthe dissipation element and the end fittings, wherein the bracingelement arranged in a bracing sleeve in at least one end fitting, anexternal contour of the bracing sleeve tapers conically in an axialdirection toward a center of the stack in a conical region, the bracingsleeve has a hole for holding a bracing element, the hole havingboundary walls configured to move toward the interior of the hole atleast in the conical region, the end fitting has a recess passingtherethrough, for holding a clamping sleeve, into which recess therespective bracing sleeve can be at least partially pushed, with theconical region being deformed, and the bracing sleeve is self-lockingsuch that the bracing sleeve is securely attached to the bracingelement.
 2. The surge arrester as claimed in claim 1, wherein the recesspassing through the end fitting is configured to be complementary to theconical region of the bracing sleeve.
 3. The surge arrester as claimedin claim 1, the bracing sleeve is slotted in the conical region, so thatthe boundary walls of the hole can move in a radially sprung manner inthe conical region.
 4. The surge arrester as claimed in claim 1, whereinthe bracing element is held by means of a bracing sleeve in the endfittings.
 5. The surge arrester as claimed in claim 1, wherein a numberof bracing elements are provided, parallel to an axis of the stack, onits outer circumference.
 6. The surge arrester as claimed in claim 5,wherein the end fittings project radially beyond the dissipationelements and, in the projecting region, have conical holes for holdingthe respective bracing sleeves.
 7. The surge arrester as claimed inclaim 1, wherein each bracing sleeve has a hole whose shape isconfigured to form an accurate fit with the external contour of therespective bracing element.
 8. The surge arrester as claimed in claim 2,the bracing sleeve is slotted in the conical region, so that theboundary walls of the hole can move in a radially sprung manner in theconical region.
 9. The surge arrester as claimed in claim 3, the bracingsleeve is slotted in the conical region, so that the boundary walls ofthe hole can move in a radially sprung manner in the conical region. 10.The surge arrester as claimed in claim 2, wherein the bracing element isheld by means of a bracing sleeve in the end fittings.
 11. The surgearrester as claimed in claim 3, wherein the bracing element is held bymeans of a bracing sleeve in the end fittings.